Garn system questions

[Rick Stanley]

Is this right so far?

#2 Fuel oil = 139,000 btu's/gal
My oil burner efficiency at last testing/tune-up=78%
My peak oil usage from 10 years of detailed delivery records=12.6 gal/day (very rare occurrence)
12.6 gallons/day X 139,000 btu's=1,751,400 btu's/day
1,751,400 btu's/day divided by 24 hours= 72,975 btu's/hour
72,975 btu's/hr X 78% efficiency= 56,920 btu's/hour

Does this mean that I only need to provide 56,920 btu's/hour from my Garn to my existing boiler?

 

[Jim K in PA]

That is one way to back into the system load requirements. A better way is to do a real heat loss analysis using the Slantfin or similar program (they are freeware). Unless you really know the consumption rate on those particular coldest days, average useage based on deliveries is not going to give you real peak numbers.

Having said that, my caclulated heat load (max) was right around 70k Btuh for my 2700 sq. ft. farmhouse that is not insulated very well (original portion built c.1815).

When is your GARN due for delivery?

 

[Rick Stanley]

That is one way to back into the system load requirements. A better way is to do a real heat loss analysis using the Slantfin or similar program (they are freeware). Unless you really know the consumption rate on those particular coldest days, average useage based on deliveries is not going to give you real peak numbers.

Yes, it is guess work. You're right. I've fooled around with those heat loss analysis programs before. It's difficult to get all of the r-factors in there. Is that a half inch gap around the fifth wooden single pane storm window from the door in the wooden ell or is it a three eighths inch? What about the replacement windows in the ground floor of the brick cape? What is the r-factor of an c.1846 Maine brick anyway? And what is in between the Maine brick and the split-board lathes (probably hemlock 3/4" maybe) that have Maine (not PA) c.1846 horse hair plaster kinda thick in places on it? Umm, could be really old corn cobs, I guess. So I'm not so sure that snazzy software can give real peak numbers either on these old farmhouses. I AM sure that the average daily oil usage between 1/20/05 and 2/2/05 was 12.6 and that was during the only winter that both units were occupied and we burned no wood. I'm going with that guess.

Having said that, my caclulated heat load (max) was right around 70k Btuh for my 2700 sq. ft. farmhouse that is not insulated very well (original portion built c.1815).

So now I need to figure out how to deliver that many btu's/hr to the existing oil boiler. How are you piping your house zone to put the 70k btuh into your house? Mine is a pressurized oil boiler with a DHW coil and separate 40 gallon DHW storage tank. I want to leave that untouched for now and just cut in with a heat exchanger so the heat from the Garn replaces the oil burner but have it controlled so the oil will come on if no Garn heat is available.

When is your GARN due for delivery?

Actually, it was already delivered from Dectra back in August, right on schedule. It's being stored at a rigging company's warehouse until I'm ready for them to bring it here and set it in place. Just got my pex yesterday. The building still needs more work. My Garn dealer has been very busy with new business, so I'm trying to educate myself regarding my system design so I can do more myself but he will ultimately design the system or at least approve what goes in. Things are slowing here now, so I have more time. We do market gardening, certified organic produce, 56 member CSA, eggs and broilers in the summer. Waaay to busy back then.

Your pics are very helpful. Looks like you are really getting it together on your project. I think it's great. I want to post pictures once things get going too. Thanks for the help!!

 

[Jim K in PA]

Yes, it is guess work. You're right. I've fooled around with those heat loss analysis programs before. It's difficult to get all of the r-factors in there. Is that a half inch gap around the fifth wooden single pane storm window from the door in the wooden ell or is it a three eighths inch? What about the replacement windows in the ground floor of the brick cape? What is the r-factor of an c.1846 Maine brick anyway? And what is in between the Maine brick and the split-board lathes (probably hemlock 3/4" maybe) that have Maine (not PA) c.1846 horse hair plaster kinda thick in places on it? Umm, could be really old corn cobs, I guess. So I'm not so sure that snazzy software can give real peak numbers either on these old farmhouses. I AM sure that the average daily oil usage between 1/20/05 and 2/2/05 was 12.6 and that was during the only winter that both units were occupied and we burned no wood. I'm going with that guess.

Oh, I agree that NONE of the calculators/estimaters are going to get it 100%, but the Slantfin program I used does account for construction material (brick, frame, frame type, etc.). I used the options as best I could and then made sure I was conservative when there was no obvious match (most of my house is plank and beam). I am sure your worst case useage is perfectly reasonable, and your GARN will keep up with whatever extra factor of comfort you want to use.

BTW - most of the horse/cow hair plaster was ripped out of our house long before we got here. unfortunately.

So now I need to figure out how to deliver that many btu's/hr to the existing oil boiler. How are you piping your house zone to put the 70k btuh into your house? Mine is a pressurized oil boiler with a DHW coil and separate 40 gallon DHW storage tank. I want to leave that untouched for now and just cut in with a heat exchanger so the heat from the Garn replaces the oil burner but have it controlled so the oil will come on if no Garn heat is available.

I also have a pressurized oil fired boiler with 4 zones of HWBB. I am t-ing in a 20 plate HX in the return line just after the circ pump. My oil furnace will be my backup for this season, and will kick in if the water temps drop below 140 (low cut in on the aquastat). I am using 1.25" oxygen barrier PEX from the GARN to the house. It is about a 120' run, with about half that underground. I am using a primary/secondary piping scheme, with closely spaced tees for the s/r lines for the house, garage and future greenhouse.

Actually, it was already delivered from Dectra back in August, right on schedule. It's being stored at a rigging company's warehouse until I'm ready for them to bring it here and set it in place. Just got my pex yesterday. The building still needs more work. My Garn dealer has been very busy with new business, so I'm trying to educate myself regarding my system design so I can do more myself but he will ultimately design the system or at least approve what goes in. Things are slowing here now, so I have more time. We do market gardening, certified organic produce, 56 member CSA, eggs and broilers in the summer. Waaay to busy back then.

Your pics are very helpful. Looks like you are really getting it together on your project. I think it's great. I want to post pictures once things get going too. Thanks for the help!!

My pleasure! I have been learning a LOT in a very short time. There is not a lot of support out there for GARN users. The Hearth members have been immeasurably helpful.

 

[TCaldwell]

Ricks, i have a 65kbtu/hr habit on a 24 hr average, i have a onicon system 10 btu meter installed on my wood loop supply and return, with that 24hr average i experience ,momentarily a 300k + btu demand , depending on how many of my 7 zones are calling simultaneously, the success is reflected by a good heat exchanger and enough flow too keep your delta t from telling your oil boiler to fire. this represents a momentary 50+deg delta t ., yes the return water might be below 100deg, all 30 gallons of it, this is insignificant when mixed with 2000gal of150+deg water stored in the garn

 

[Rick Stanley]

Jim and Tom,

Thanks a million. Good input.

Do the pumps on both loops come on at the same time when the oil boiler temp falls below say 140 or whatever, instead of the oil burner firing? Is that the idea? OR Does one or both run all of the time?

Here's another probably dumber question: In general, where does it make the most sense for the pumps and exchanger to be? Near the oil boiler? Near the Garn 170 ft away? Some of each? I got no clue.

Thanks,
Rick

 

[Jim K in PA]

Ricks, i have a 65kbtu/hr habit on a 24 hr average, i have a onicon system 10 btu meter installed on my wood loop supply and return, with that 24hr average i experience ,momentarily a 300k + btu demand , depending on how many of my 7 zones are calling simultaneously, the success is reflected by a good heat exchanger and enough flow too keep your delta t from telling your oil boiler to fire. this represents a momentary 50+deg delta t ., yes the return water might be below 100deg, all 30 gallons of it, this is insignificant when mixed with 2000gal of150+deg water stored in the garn

TC - do you use a flow meter with the Onicon 10? OTher than measurement, what do you use it for? What do they cost?

Also - what HX are you using?

If you have a web page with your specs and layout, would you share it?

Thanks.

 

[Nofossil]

As mentioned above, averages don't tell you much about the coldest day. A reasonable rule of thumb is that your coldest day is usually about twice your heating season average.

60,000 BTU/hr doesn't seem unreasonable for a peak demand. Instantaneous peaks (like DHW) don't matter - it's the highest 12 hour demand that's more useful in sizing your system.

Slantfin is a good tool, but in my experience everyone has incentive to err on the side of overestimating the actual loss. I'd do the Slantfin and cross-check it based on your actual fuel consumption, using the 2x factor. If they're close, go with it.

Nearly all systems, fossil and wood, are oversized. If your oil system is bigger than it needs to be, you'll never notice. If it's too small, you'll notice right away and be pretty upset with the installer. What would you do if you were the installer?

 

[Rick Stanley]

As mentioned above, averages don't tell you much about the coldest day. A reasonable rule of thumb is that your coldest day is usually about twice your heating season average.

60,000 BTU/hr doesn't seem unreasonable for a peak demand. Instantaneous peaks (like DHW) don't matter - it's the highest 12 hour demand that's more useful in sizing your system.

Slantfin is a good tool, but in my experience everyone has incentive to err on the side of overestimating the actual loss. I'd do the Slantfin and cross-check it based on your actual fuel consumption, using the 2x factor. If they're close, go with it.

Yup, sounds right. You guys know more than I. I have a Garn 2000 and I'm using 170 ft. (one way), of 1-1/4 in pex, so I 'm oversized so far for heating the house and that was the intent. It's an expandable system. Want to have capacity enough to cover many future plans and options and buildings. I'll do the Slantfin and double it if it's close to the fuel consumption to size the pumps and heat exchanger when the time comes. More pressing at the moment, is where the pumps and heat exchanger should be and how they will be controlled so I'll know what else to put into the trench besides the pex. What do you say?

Nearly all systems, fossil and wood, are oversized. If your oil system is bigger than it needs to be, you'll never notice. If it's too small, you'll notice right away and be pretty upset with the installer. What would you do if you were the installer?

The way it's looking right now, I AM the installer :bug:

 

[Jim K in PA]

Jim and Tom,

Thanks a million. Good input.

Do the pumps on both loops come on at the same time when the oil boiler temp falls below say 140 or whatever, instead of the oil burner firing? Is that the idea? OR Does one or both run all of the time?

Here's another probably dumber question: In general, where does it make the most sense for the pumps and exchanger to be? Near the oil boiler? Near the Garn 170 ft away? Some of each? I got no clue.

Thanks,
Rick

Rick - Both pumps should come on whenever there is a call for heat from any of the zones. With an HX, there is not much sense in circulating the secondary pump when there is no heat load. No need to keep either running constantly, AFAIK.

The HX for the oil furnace should be located near the furnace, and plumbed just downstream from the oil burner's circ pump. I am T-ing into my return line where my pump is currently located, but adding a bypass circuit and shutoffs for the lines to the HX so I can bypass it if I need to.

 

[TCaldwell]

Ricks/Jim, I run both loops 24/7, with a long pex run and stagnant water cooling down,i am concerned that period of cool supply will kick the oil boiler aquastat on, i have been thinking about a taco variable speed setpoint circulator on the oil side, the speed would be controlled by a temp diferential recorded near the hx on the supply and return. Not to complicate things i have 2 taco 0014's on my wood loop, the net result is 14.5gpm at 6psi, one circ is at the garn specified loc. the second one is on the return side of the hx, basically in the middle of the loop,in the summer, low demand i remove the one on the return side, 10gpm at 7.5psi. If i were to reinstall my garn it would be with alot less wood loop piping, alot closer to the house, affording less headloss and potential heatloss., with a smaller pump. as it is set up ,i run the system down to 135deg without fear of the oil boiler kicking on. the onicon system 10 displays at a toggle flow rate, supply temp,return temp, total gallons through the meter, actual btus consumed realtime and total btus consumed for a given period. all totals are resetable. the unit can be configured with a 4/20 milliamp signal output and modbus communication. starts at $1200. comes with a calibration cert. the hx i bought from dectra it is a 30 plate flatplate with 1.5inch mip ftgs, i think it is a mp102030, it was about $2000.

 

[Rick Stanley]

Nofossil,
This is a re-post of part of a previous question. I feared it got lost in the blue quote box:
Yup, sounds right. You guys know more than I. I have a Garn 2000 and I’m using 170 ft. (one way), of 1-1/4 in pex, so I ‘m oversized so far for heating the house and that was the intent. It’s an expandable system. Want to have capacity enough to cover many future plans and options and buildings. I’ll do the Slantfin and double it if it’s close to the fuel consumption to size the pumps and heat exchanger when the time comes. More pressing at the moment, is where the pumps and heat exchanger should be and how they will be controlled so I’ll know what else to put into the trench besides the pex. What do you say?

Here's what I know so far: The building that the garn is going into has it's own electric so no buried power lines are needed. There's no water out there, so I want to bury a 1in water line with the pex. The only other thing that I can think of is that if there ends up being a pump on the Garn end that needs to be controlled from the house end(oil boiler), I'll need wiring for that. So I guess, bury a second 1in poly-pipe to snake, um, what? Thermostat wire? I don't know.

 

[Nofossil]

As far as I know, no one has EVER regretted burying an extra black plastic pipe. You never know what you'll want to pull through it.

I can't comment on the rest without some sort of proposed diagram. Do you have a sketch that you could scan or photograph?

 

[Rick Stanley]

I put a link on my signature, hope it works. It's 200 ft between boilers 170 of it underground 1-1/4"

 

[Nofossil]

I'm going out on a limb here, but I think it makes sense to put the Garn circ near the Garn, and put the HX and the load circ in the house.

The load circ would presumably be wired to run whenever there is a heat demand. It appears that the load circ would be the existing circ for the existing boiler, so it might already be set up to do that anyway.

I don't know how the Garn is intended to work, but at the very least you'd want the Garn circ to run whenever the load circ runs.

There might be some benefit to setting up a relay to disable the existing boiler any time that the Garn is hot. If you don't do that, the existing boiler will start any time there's heat demand and run for a few minutes until the hot water from the Garn reaches it.

I'd expect that the Garn manual would have some details on how they intend their schematic to work.

 

[TCaldwell]

ricks, there is a bung on the garn for a aquastat that you set for a temp to power your wood circ and oil boiler system circ together if you choose. you will need a conduit from wood circ to oil boiler circ, maybe a spare conduit for monitoring hardware and you already have a water line.last night i forgot, the heatexchanger is close to the oil boiler.

 

[Jim K in PA]

I'm going out on a limb here, but I think it makes sense to put the Garn circ near the Garn, and put the HX and the load circ in the house.

That is what I am doing. The primary loop will run whenever the house loop pump runs. I am installing the house loop pump near the primary loop in the garage (near the GARN). The HX is going in the house near the oil burner. The load pump is in the return side and is piped in just before the HX. That will circulate the coolest water through the HX before it goes back into the oil furnace.

The load circ would presumably be wired to run whenever there is a heat demand. It appears that the load circ would be the existing circ for the existing boiler, so it might already be set up to do that anyway.

That is how mine is set up. My existing TACO 007 will be just about maxed out with the HX and the load circuits (for head loss), but I only plan to use it in this configuration for a couple of seasons. I will upgrage in the future to a multi-pump setup for the load (zones) and eliminate the zone valves.

I don't know how the Garn is intended to work, but at the very least you'd want the Garn circ to run whenever the load circ runs.

Correct. I am adding an Aquastat in the circ line on the load side of the HX. It will be set to kick on the house loop pump AND the GARN primary pump at a temp at least 20 degrees higher than I have the oil furnace Aquastat set for. That should allow for any delay in warm water reaching the HX.

There might be some benefit to setting up a relay to disable the existing boiler any time that the Garn is hot. If you don't do that, the existing boiler will start any time there's heat demand and run for a few minutes until the hot water from the Garn reaches it.

I think if you do the above with the second Aquastat, you have accomplished this.

I'd expect that the Garn manual would have some details on how they intend their schematic to work.

Oh, how I WISH this were true. The diagram you see in Rick's link is the sum total of the detail that Dectra provides in terms of connection instructions. Apparently they have deleted a substantial amount of detail from their earlier manuals.

I will have some more pictures posted on my site soon.

 

[Jim K in PA]

ricks, there is a bung on the garn for a aquastat that you set for a temp to power your wood circ and oil boiler system circ together if you choose. you will need a conduit from wood circ to oil boiler circ, maybe a spare conduit for monitoring hardware and you already have a water line.last night i forgot, the heatexchanger is close to the oil boiler.

Is that what the bung next to the water temp gauge is intended for? I am going to use that for a sight glass, and put the Aquastat temp sensor in the primary pipe loop.

Rick - I would install at least a 1.5" diameter electrical conduit in addition to the water line (and S/R lines). I am actually installing two runs of conduit - one for high voltage controls, and one for low voltage and data. At the very least I want to put a land line in the garage (telephone).

 

[Rick Stanley]

Jim, what are you using for conduit and how are you pulling the wires through?

 

[Jim K in PA]

Jim, what are you using for conduit and how are you pulling the wires through?

I am using "standard" gray schedule 40 PVC conduit (available at Lowes, etc.). Make sure you use their long turn 90s or 45s, not standard plumbing fittings.

You start pulling by tying a light piece of cloth or foam to a string, then pull it through the pipe with a shop-vac. Then use the string to pull the line(s) you need through the pipe. I always add another chase string to the wire bundle in case I need to pull another run later on.

 

[Rick Stanley]

Got some questions on tying in my HX. Here are some shots first. These should be supply and return headers.

 

[Rick Stanley]

Somebody said to cut the boiler away here(in the supply pipe) and add tees there and in the return and add a pump. Not a very handy spot to work in. Above the boiler in 6 inches of space below ceiling. Plus, the plan there was to let the boiler go cold and I didn't want to do that because it is my DHW (coil) supply at the moment and it's kind of an old boiler and I didn't want it to leak.

 

[Rick Stanley]

Another plan was to cut two close tees in here and be done with it. Might be simple enough..................

 

[Jim K in PA]

Another plan was to cut two close tees in here and be done with it. Might be simple enough..................

Rick, if that is your return leg, that is where I would (and did) put in the close Tees and valves. Here is my splice:

I should have some more pics posted of the HX connections and piping soon. I'll also have my control schematic finalized and posted soon, too.

 

[Rick Stanley]

Also, it was suggested that both headers and the boiler be made into a big primary loop with it's own pump. The question I have there is: can I accomplish that by connecting the plugged end of the return header shown here, to the drain end of the supply header also shown here? It seems like it would be easy to do because both ends are on the same side of the boiler and face the same direction which is the same direction the pipes from the HX will come from.

Any comments or suggestions? Thank you!!